PakledHostage Posted January 11, 2015 Share Posted January 11, 2015 Incidentally while I was looking for this video I found another. There has been some discussion here about how they keep the barge stable with mostly guesses on how they do it. I found this video stating they use thrusters.They may well control the barge's lateral position using thrusters. They can't control the vertical position of the deck that way, however. That is the point that people are speculating about. The deck's vertical position is governed by the waves because the barge is floating on them. Some multihull vessels actively damp the up/down motion by modulating buoyancy, but SpaceX's barge is not a multihull vessel with that capability. Link to comment Share on other sites More sharing options...
merendel Posted January 11, 2015 Share Posted January 11, 2015 According to the youtube video the fins rotate to help steer the craft. did anybody else LOL at 1:41? the point where the dragon capsule separates and gently drifts ahead of the clearly still thrusting upper stage with no visible thrust of its own? aside from how horribly dangerous separating would be with a still thrusting rocket behind you I don't think it works that way Link to comment Share on other sites More sharing options...
astropapi1 Posted January 11, 2015 Share Posted January 11, 2015 did anybody else LOL at 1:41? the point where the dragon capsule separates and gently drifts ahead of the clearly still thrusting upper stage with no visible thrust of its own? aside from how horribly dangerous separating would be with a still thrusting rocket behind you I don't think it works that way I was watching the video half-asleep and had to pause for a second and return after a "wait, what?!" moment. It's funny how small the Earth looks at about 1:10 too, kinda like Kerbin. I love it when people make animation mistakes like these. Was it really that hard to look up the launch sequence before rendering the whole thing? Link to comment Share on other sites More sharing options...
Leszek Posted January 11, 2015 Share Posted January 11, 2015 did anybody else LOL at 1:41? the point where the dragon capsule separates and gently drifts ahead of the clearly still thrusting upper stage with no visible thrust of its own? aside from how horribly dangerous separating would be with a still thrusting rocket behind you I don't think it works that way Yes, you see that sort of thing with radial SRB sep but not on a inline second stage which (correct me if I am wrong) is liquid fueled. Link to comment Share on other sites More sharing options...
merendel Posted January 11, 2015 Share Posted January 11, 2015 Yes, you see that sort of thing with radial SRB sep but not on a inline second stage which (correct me if I am wrong) is liquid fueled.Not sure you'd want to release even a radial SRB with it still runing unless you expect the pair to not run out at the same time and it would still be dangerous. I was more refering to the fact that the pod was able to get away from the thrusting stage. Even if you separated with explosive bolts or something that throws it forward unless the pod is producing thrust with the same or greater TWR that spent stage would accelerate right back up its tailpipe a moment later. Just pokeing fun at the fact that the animator clearly didn't get a reality check done before sending that off to the media distribution department and nobody else along the chain noticed while there was time to fix it. Link to comment Share on other sites More sharing options...
Nibb31 Posted January 11, 2015 Share Posted January 11, 2015 The Shuttle SRBs were jettisonned while there was still residual combustion. SRB don't just die down all at once.However, for a liquid engine, you would want to wait until the combustion is finished before separating. Link to comment Share on other sites More sharing options...
merendel Posted January 11, 2015 Share Posted January 11, 2015 The Shuttle SRBs were jettisonned while there was still residual combustion. SRB don't just die down all at once.However, for a liquid engine, you would want to wait until the combustion is finished before separating.Good point I was thinking about that wrong. Stuff still leaking out the back =/= still producing meaningful thrust. I was thinking leszek ment leting them go while they were still producing considerable thrust which would be bad as you can no longer controll where they'd go. particularly bad if they do the KSP trick of moveing out just slightly then convergeing just ahead of where they were released, right above or in the upper portions of the main craft. However you make a good point there would still be residual burnoff spiting burning material out the back even if it was no longer able to produce any significant TWR, thats probably what laszek ment.although I agree still laughable for a liquid engine. Link to comment Share on other sites More sharing options...
CptRichardson Posted January 11, 2015 Share Posted January 11, 2015 I was watching the video half-asleep and had to pause for a second and return after a "wait, what?!" moment. It's funny how small the Earth looks at about 1:10 too, kinda like Kerbin. I love it when people make animation mistakes like these. Was it really that hard to look up the launch sequence before rendering the whole thing?Rendered in KSP? Link to comment Share on other sites More sharing options...
benzman Posted January 11, 2015 Share Posted January 11, 2015 Good point I was thinking about that wrong. Stuff still leaking out the back =/= still producing meaningful thrust. I was thinking leszek ment leting them go while they were still producing considerable thrust which would be bad as you can no longer controll where they'd go. particularly bad if they do the KSP trick of moveing out just slightly then convergeing just ahead of where they were released, right above or in the upper portions of the main craft. However you make a good point there would still be residual burnoff spiting burning material out the back even if it was no longer able to produce any significant TWR, thats probably what laszek ment.although I agree still laughable for a liquid engine.According to Mike Mullane's book 'Riding Rockets' SRBSEP for the shuttle occurs when the internal gas pressure drops to 50 PSI. I suppose that unlike liquid engines that can be shut down to zero thrust virtually instantly, solids burn the majority of their fuel and then take a while to fizzle out. So it would make sense to drop them when their thrust was no longer enough to overcome their aerodynamic drag. Link to comment Share on other sites More sharing options...
softweir Posted January 11, 2015 Share Posted January 11, 2015 (edited) Rendered in KSP?More likely Orbiter - that's better suited for animation production than KSP thanks to a very mature and extensive set of mods.According to Mike Mullane's book 'Riding Rockets' SRBSEP for the shuttle occurs when the internal gas pressure drops to 50 PSI. I suppose that unlike liquid engines that can be shut down to zero thrust virtually instantly, solids burn the majority of their fuel and then take a while to fizzle out. So it would make sense to drop them when their thrust was no longer enough to overcome their aerodynamic drag.The fuel plugs are designed to produce a varying thrust curve, with a slow, controlled drop in thrust towards the end of the burn. Edited January 11, 2015 by softweir Link to comment Share on other sites More sharing options...
Airlock Posted January 11, 2015 Share Posted January 11, 2015 ASDS back in port. http://spaceflightnow.com/2015/01/11/photos-spacexs-rocket-landing-platform-back-in-port/Photos of the barge show signs of blast and burn damage to cargo containers and possible wreckage from the rocket covered by tarps on the platform’s deck. The rest of the vessel appeared undamaged./r/SpaceX thinks this is how the landing went. Link to comment Share on other sites More sharing options...
Nuke Posted January 11, 2015 Share Posted January 11, 2015 (edited) looks like it missed the center. i think you need more precise tracking for the final part of the landing, something video based. for example have tracking cameras on the barge set up to track the rocket's motor plume, calculate local position and transmit course corrections up to the rocket.They may well control the barge's lateral position using thrusters. They can't control the vertical position of the deck that way, however. That is the point that people are speculating about. The deck's vertical position is governed by the waves because the barge is floating on them. Some multihull vessels actively damp the up/down motion by modulating buoyancy, but SpaceX's barge is not a multihull vessel with that capability.it makes me wonder if you cant correct for wave motion in software. have some accelerometers on the barge keeping track of wave motion. transmit that data up to the landing rocket. final touchdown would then begin at the top of the wave and complete at the bottom of the wave. that way you never have to worry about the waves slamming the barge into the rocket. Edited January 11, 2015 by Nuke Link to comment Share on other sites More sharing options...
AngelLestat Posted January 11, 2015 Share Posted January 11, 2015 (edited) I am not sure what kind of guiding system it uses now. But they have plenty to choose. GPS, radar, infrared, ILS (or something similar to transmit from base to the rocket the corrections needed), laser, etc.Or maybe the tranking system is optimal but they lack on precision from the rocket control systems.EDIT: or the algorithm is wrong... Is time to copy the mechjeb code! Edited January 11, 2015 by AngelLestat Link to comment Share on other sites More sharing options...
sgt_flyer Posted January 11, 2015 Share Posted January 11, 2015 (edited) looks like it missed the center. i think you need more precise tracking for the final part of the landing, something video based. for example have tracking cameras on the barge set up to track the rocket's motor plume, calculate local position and transmit course corrections up to the rocket.it makes me wonder if you cant correct for wave motion in software. have some accelerometers on the barge keeping track of wave motion. transmit that data up to the landing rocket. final touchdown would then begin at the top of the wave and complete at the bottom of the wave. that way you never have to worry about the waves slamming the barge into the rocket.i think the landing precision is not in question - they stated the rocket ran out of hydraulic fluid to drive the grid fins before the landing - so the rocket could not steer itself during the landing attempt. they'll have 50% more hydraulic fluid for the next attempt (especially as all minor trajectory corrections will happen in the last minutes of the flight - the grid fins are put to heavy use during these last few moments) Edited January 11, 2015 by sgt_flyer Link to comment Share on other sites More sharing options...
Leszek Posted January 12, 2015 Share Posted January 12, 2015 (edited) As was pointed out, the loss of control of the fins due to running out of hydraulic fluid explains the miss.Visual landing aids wouldn't have helped in this situation, it was night and the area was foggy.I am not sure what kind of guiding system it uses now. But they have plenty to choose. GPS, radar, infrared, ILS (or something similar to transmit from base to the rocket the corrections needed), laser, etc.Or maybe the tranking system is optimal but they lack on precision from the rocket control systems.EDIT: or the algorithm is wrong... Is time to copy the mechjeb code!I have no idea what they actually used but I would put my money on an ILS based system myself. The technology is mature and reliable. Commercial plains use it to control the autopilot for autoland functionality is rough weather. The system is attached to the barge and thus would roll right and left with the physical barge. Also the DME (Distance Measuring Equipment) would detect the barge rise and fall with the waves if it is sensitive enough. (Typically the ones in commercial aircraft report to the nearest 10th of a nautical mile. I am not sure what accuracy they have beyond that. The system works by pinging the DME equipment and timing the delay for a reply. I don't know how sensitive they can get.) Assuming the DME is sensitive enough it means the rocket computer could track the rise and fall and rotation of the barge and make corrections as required. Edited January 12, 2015 by Leszek Format change to make things more clear. Link to comment Share on other sites More sharing options...
Nuke Posted January 12, 2015 Share Posted January 12, 2015 (edited) night is the perfect condition for optical based target tracking. it gets rid of most of the noise that would need to be processed out before doing blob detection. use wavelength matched filters and lights can be effective. uv light can penetrate clouds and fog sufficiently to find the pad in the final phase of landing. in daylight, chances are other than the sun the rocket plume would be the brightest spot in the sky, especially on infra red. just cause you cant see it doesnt mean computer vision systems cant. but i admit that if you cant control the thing then all this tracking gear would be for nothing. dont you also need hydraulic power for the gimbal systems as well? seems for the final phase the gimbals would take over from the drag fins since there would not be sufficient airflow over them to be of use. Edited January 12, 2015 by Nuke Link to comment Share on other sites More sharing options...
maccollo Posted January 12, 2015 Share Posted January 12, 2015 Video of one of the pieces that survived being recovered. "Hard landing" looks like an understatement. This thing used to be a tube, now it's pancake. Link to comment Share on other sites More sharing options...
bigdad84 Posted January 12, 2015 Share Posted January 12, 2015 ASDS back in port. http://spaceflightnow.com/2015/01/11/photos-spacexs-rocket-landing-platform-back-in-port/http://spaceflightnow.com/wp-content/uploads/2015/01/asds_2.jpg/r/SpaceX thinks this is how the landing went. http://i.imgur.com/zYGDDBO.gifI laughed way hard at the GIF. They were so close though! Link to comment Share on other sites More sharing options...
AngelLestat Posted January 12, 2015 Share Posted January 12, 2015 the benefic with ILS (or similar system) is that you remove complexity from the rocket, you may have plenty of sensors close to the landing site, traking the rocket and sending just the correction needed.For example if you need to include all different sensors in a rocket, you need track the wind speed, exact position, fast procesors, etc. When the rocket already has to deal with enoght hard conditions and control systems. Link to comment Share on other sites More sharing options...
Leszek Posted January 12, 2015 Share Posted January 12, 2015 the benefic with ILS (or similar system) is that you remove complexity from the rocket, you may have plenty of sensors close to the landing site, traking the rocket and sending just the correction needed.For example if you need to include all different sensors in a rocket, you need track the wind speed, exact position, fast procesors, etc. When the rocket already has to deal with enoght hard conditions and control systems.ILS doesn't track the rocket in any way. It sends a radio beam up and the rocket follows it down. The barge just needs some antennas. The DME is the only part that would interact with the rocket, and it just responds to a ping from the rocket. However the equipment is simple and reliable and off the shelf. Even on the rocket side the ILS equipment is not complicated. If your smartphones could tune to FM just above broadcast range, the app to turn your smartphone into an ILS device would be free and simple.Though you are right, you don't need to know the wind or anything, you just follow the beam down. Link to comment Share on other sites More sharing options...
RainDreamer Posted January 12, 2015 Share Posted January 12, 2015 For some reasons the media mainly talk about the failure of the landing, instead of how the launch is successful, Dragon going to ISS, and they actually hit the mark.And about the images of the barge, darn, I know rocket engine is hot, but looking at how the steel container melted does put it into perspective.How far did the first stage miss the X? Link to comment Share on other sites More sharing options...
Ralathon Posted January 12, 2015 Share Posted January 12, 2015 Video of one of the pieces that survived being recovered. "Hard landing" looks like an understatement. This thing used to be a tube, now it's pancake.Doesn't have to be a hard landing to crumple a stage like that. Rockets are made as flimsy and light as possible after all. Heck, some second stages would crumple under their own weight if empty, the only thing keeping them intact is the internal pressure of the fuel.So I'm not at all surprised that the first stage crumples like a tin can when hitting a surface at 20ish m/s Link to comment Share on other sites More sharing options...
Albert VDS Posted January 12, 2015 Share Posted January 12, 2015 Video of one of the pieces that survived being recovered. "Hard landing" looks like an understatement. This thing used to be a tube, now it's pancake.http://youtu.be/ZeqKacuxyOITo be fair, a rocket stage isn't build for handling landing impacts but for lightness.So, relatively speaking, it wouldn't take a whole lot to make it into a pancake. Link to comment Share on other sites More sharing options...
Camacha Posted January 12, 2015 Share Posted January 12, 2015 Let us be more specific: a rocket stage is not built for handling forces coming from the side, only coming from the bottom/top (i.e. in line with the engine thrust). If the thing fell over, a small knock in the wrong place could do a lot of damage. Landing it straight, however, would do no harm. Link to comment Share on other sites More sharing options...
PlonioFludrasco Posted January 12, 2015 Share Posted January 12, 2015 Dragon is going to be captured in few minutes!!! Streaming on NASA TV Link to comment Share on other sites More sharing options...
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